Pyrotechnic coiled delay cord assembly for hand grenade fuze

ABSTRACT

An improved hand grenade fuze that has an out-of-line metal sheathed pyrotechnic delay cord helically wound about a mandrel. The delay cord forms the threads of a delay-detonator assembly which cannot be screwed into the fuze head unless the delay cord is present thereby insuring the presence of the delay element.

United States Patent Lerman 1 Dec. 12, 1972 [54] PYROTECHNIC COILEDDELAY CORD FOREIGN PATENTS OR APPLICATIONS ASSEMBLY FOR HAND GRENADE305,056 8/1916 Germany ..l02/64 FUZE 593,396 5/1925 France ..I02/64 [72]Inventor: Russell E. Lerman, Morris, NJ.

Primary Examiner-Verlin R. Pendegrass Asslgneei The United states Amen"as Attorney-Harry M. Saragovitz, Edward J. Kelly and represented by theSecretary of the H b B l Army [22] Filed: Feb. 8, 1971 [57] ABSTRACT Animproved hand grenade fuze that has an out-of- [21] Appl' 113416 linemetal sheathed pyrotechnic delay cord helically wound about a mandrel.The delay cord forms the 52 US. Cl ..l02/64, 102/85 threads of adelay-detonawr assembly which cannot 51] 1111. c1. ..F42b 27/00, F42c9/10 be Screwed into the fuze head unless the delay cord is [58] Fieldof Search ..l02/64, 65 -72 85 thereby insuring the Presence of the delayment. [56] Referen Cited 3 Claims, 8 Drawing Figures UNITED STATESPATENTS 2,687,093 8/1954 Botts .L.l02/24 R I 22 74 6 '9 27 I8 2a 42 2146 4e l p aw: 50 I I t ,1: h I Io-1: I 2' '1 i l I a a l 3 o o I a IPATENTEUUEC 12 I972 SHEET 2 BF 2 INVENTOR.

BY! RUSSELLE. LERMAN FIG. 7

mmngnnzn 12 m2 3; 705 552 SHEET 1 0F 2 H INVENTOR) BY,- RUSSELL E.LERMAN PYROTECI-INIC COILED DELAY CORD ASSEMBLY FOR HAND GRENADE FUZEThe invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to an improved delayfuze for hand grenades or similar explosive devices which require afixed time delay after initiation of the fuze by a percussion primer.

Difficulty has been encountered with prior art grenades that utilized inline delay columns to initiate a detonator. One of the problems with theaforementioned prior art has been the danger that the user of the devicehas been subjected to when a delay column was inadvertently left out ofthe grenade during the manufacturing, or where the delay column wasimproperly constructed. In such instances the malfunction could resultin a grenade failing premature rather than failing safe. The primer, insuch cases where there is either a missing or defective delay column,directly activates the detonator without the required delay. The currentstateof-the art manufacture of delay column requires the pressing ofpyrotechnic powder in metal tubes at controlled consolidation pressures.Since this is a difficult operation to always perform because some delaycolumns are produced which have cracks in the powder material, or wherevoids are caused by powdering. If

such a defective delay column is not detected in the initial inspection,the grenade will expose the user to the possibility of prematureexplosion or have erratic time delays. In order to overcome theaforementioned dangers expensive inspection procedures such as x-rayphotography are required to eliminate those devices with either missingor defective delay columns.

Another problem encountered with the in-line primer, delay column,detonator construction is the requirement that the delay column beloaded through the top of the fuze head. This top loading operationrequires the use of a separate primer assembly which must be assembledinto the fuze head on top of the delay column after the latter has beenfilled.

Additional difficulty encountered with present grenades has been due tothe need for high energy primers to reliably initiate the pyrotechnicdelay column. The use of high energy primers has resulted in additionalmalfunction caused by blown primers, and primer assembly and crackedfuze housings.

Pyrotechnic columns whether in the pressed or extruded metal sheathedform tend to burn more accurately as the burning rate is increased.Prior art pressed delay columns are limited in their accuracy because ofthe limited length of column that can be incorporated in the in-linefuze design. In the present invention this limitation in length isovercome by making the delay column in the form of a coil and usingpyrotechnic material having a faster and more accurate burning rate. Theextruded metal cord containing pyrotechnic mixtures may be obtainedcommercially in a variety of burning rates.

SUMMARY OF THE INVENTION The present invention relates to a hand grenadefuze which will prevent premature detonation due to inadpyrotechnicmaterial which can be activated by a lower energy primer.

One of the objects of this invention is to provide a hand grenade whichis cheaper to manufacture because it requires less inspection and fewerparts.

Another object of this invention is to insure that in the event of amalfunction after the grenade is activated that it will fail safe ratherthan fail premature.

Another object of this invention is to eliminate the need for a separateprimer holder assembly.

Another object of this invention is to reduce the erratic times fordelay which occur in prior art in-line delay column type fuzes.

Another object of this invention is to reduce the number of malfunctionsoccurring in hand grenades due to blown primers and/or cracked housingsby the use of a lower energy primer.

Another object of this invention is to eliminate inad vertently omitteddelay columns by making it impossible to assemble the fuze if the delaycolumn is not present.

A further object of this invention is to eliminate the need to percentx-ray assembled grenades in order to detect missing delay columns.

For better understanding of the present invention, together with otherand further objects thereof,

reference is made to the following description taken in connection withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional elevation of agrenade fuze assembly, striking means, and safety means according to theinvention.

FIG. 2 is an elevational view of the mandrel illustrated in FIG. 1.

FIG. 3 is a sectional view of the mandrel taken along line 33 in FIG. 2.

FIG. 4 is an elevational view of the mandrelpyrotechnic delay cordsub-assembly as illustrated in FIG. 1.

FIG. 5 is a sectional view of the mandrel-pyrotechnic delay cordsub-assembly taken along line 5-5 in FIG. 4.

FIG. 6 is an enlarged partial sectional view of the lower right handcomer of the mandrel-pyrotechnic delay cord sub-assembly as illustratedin FIG. 5.

FIG. 7 is an elevational view, and partial sectional view of thecombined detonator-delay assembly consisting of a mandrel-pyrotechnicdelay cord sub-assembly crimped to a detonator sub-assembly asillustrated in FIG. 1.

FIG. 8 is a plan view of the combined detonatordelay assembly of themandrel-pyrotechnic delay cord sub-assembly and the detonatorsub-assembly, taken along line 8-8 as illustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in FIG. 1, ahollow fuze head has a first central bore 11, axially aligned therewithand connected thereto is a second primer bore 12 of smaller diameter;flash hole 13 of smaller diameter than primer bore 12 is concentricallyconnected therewith; primer bore 12 is intermediate to the first centralbore 11 and flash hole 13. A threaded bore 14 is axially aligned withthe flash hole 13; flash hole 13 is intermediate to the primer bore 12and the threaded bore 14. Concentrically located with the lower half ofthe threaded bore 14 is a threaded boss 20. The complete fuze assemblyas illustrated in FIG. 1 is screwed to a grenade housing 21 by means ofthe threaded boss 20, the grenade housing contains an explosive charge(not shown).

A percussion primer 22 is firmly held in primer bore 12 by a lip 24produced by a crimping tool (not shown) which extrudes a portion of thefuze head material immediately adjacent to the primer bore over andcircumambient the outer periphery of the primer 22.

A safety lever 36 has an arcuate end 17 which is positioned under pivotpin 18, the middle section of the safety lever 36 is held firmlyattached to the fuze head 10 by a striker retaining safety pin 32 whichis slidably positioned in a fuze pin aperture 30 and a concentricallypositioned safety lever pin aperture 31. The combination of the pivotpin 18 restraint upon the arcuate extension 17 and the striker retainingpin 32 restraint upon the striker lever 34 prevents the safety lever 36from being inadvertently moved.

A striker lever 34 is pivotally held by a striker pivot pin 28, thestriker pivot pin is firmly held by the interference fit between astriker pivot pin aperture 27 and the striker pivot pin 28. The strikerpivot pin aperture 27 horizontally located in the fuze head 10, has itsaxis perpendicular to the longitudinal axis of the grenade fuzeassembly. A striker spring 26 is also supported by the striker pivot pin28 and spring loaded to exert a rotational force against the strikerlever 34 when the safety lever 36 is intentionally released. Removal ofthe safety pin 32 and release of the safety lever 36 by the user willpermit the spring loaded striker lever 34 to rotate about striker pivotpin 28, throwing off and separating safety lever 36 from the fuze head10, permitting striker lever 34 to forcibly impact upon the percussionprimer 22.

A cylindrical mandrel 38 as shown in FIG. 2 and 3 has a helically cutmandrel thread 40 in its outer periphery.

A metallic sheath pyrotechnic delay cord 42 is tightly wound in themandrel helical threads 40 to form a mandrel-delay cord sub-assembly asshown in FIGS. 4 and 5. The enlarged sectional view of FIG. 6 shows themandrel 38 helically wound with an aluminum metal sheath 43 surroundingan inner pyrotechnic delay composition having a burning rate ofapproximately 2 inches per second as a core 44.

FIGS. 7 & 8 show a detonator-delay assembly wherein themandrel-pyrotechnic delay cord sub-assembly as illustrated in FIGS. 4, 5and 6 is partially inserted into an aluminum detonator case 46; thedetonator case 46 material is crimped over the convoluted delay cord 42and mandrel 38 so as to leave a safety gap 48 intermediate to the lowerend of the mandrel 38 and the top of a first detonating material 50 oflead styphnate, the balance of the detonator case is composed of asecond detonating layer 51 of lead azide, and a third detonating layer52 of cyclonite; The aforementioned detonator-delay assembly is screwedinto the threaded bore 14 using the partially projecting delay cord 42of the mandrel-pyrotechnic delay cord assembly as the mating threads.The presence of the crimped detonator case 46 about themandrelpyrotechnic sub-assembly acts as a predetermined stop for thedistance that the mandrel-delay assembly will travel into threaded bore14, a gas chamber 15 is provided for the expanding gases generated bythe primer 12 after initiation by striker lever 34. The mandreldelayassembly prevents the direct initiation of the detonator by the primerother than through the delay cord.

From the above description it will be evident that the present inventioninsures that a delay cord will be present when the fuze is assembled,because the detonator cannot be attached to the fuze head without thedelay cord acting as the mating thread. This improved fuze eliminatesthe need for expensive x-ray inspection techniques, and permits the fuzeto fail safe rather than fail premature. This invention permits the useof lower energy primers because the aforementioned design allows thedelay element to be screwed up to the output end of the primer therebyreducing the probability of blown primers, cracked fuze heads and duds.

I wish it to be understood that I do not desire to be limited to theexact detail of construction shown and described for obviousmodifications will occur to a person skilled in the art.

What is claimed is:

1. An improved hand grenade fuze of the type wherein said fuze has meansfor holding a percussion primer, means for channeling gases from saidprimer to a gas chamber, means for operatively striking said percussionprimer, safety means for preventing said striking means from operatinginadvertently, means for attaching said fuze to a grenade body, and adetonating means for actuating a main explosive charge, wherein theimprovement comprises:

a fuze head having'a threaded bore communicating with said primer;

a pyrotechnic delay cord;

a solid cylindrical mandrel having a peripheral helical thread on itslongitudinal surface extending from one end of said mandrel to the otherend;

a mandrel-delay cord sub-assembly consisting of said delay cord woundupon said peripheral helical thread;

a detonator-delay assembly having said detonating means attached to saidmandrel-delay cord sub-assembly so that said mandrel-delay cordsub-assembly partially protrudes out of said detonating means providinga screw like extention, said delay cord interfitably engages saidthreaded bore when said detonator-delay assembly is screwed into saidthreaded bore, said detonating means having a shoulder which permitssaid mandrel-delay cord assembly to be screwed into said threaded borefor a predetermined fixed distance.

2. An improved hand grenade fuze as recited in claim 1 wherein thepyrotechnic delay cord comprises:

delay core; and

a metal sheath longitudinally circumambient to said delay corecomposition having open ends exposing said delay core to said primer onsaid one end of said mandrel, and exposing said delay core to saiddetonator on said other end of said mandrel.

3. An improved hand grenade fuze as described in claim 2 wherein saidmetal sheath is aluminum.

1. An improved hand grenade fuze of the type wherein said fuze has meansfor holding a percussion primer, means for channeling gases from saidprimer to a gas chamber, meanS for operatively striking said percussionprimer, safety means for preventing said striking means from operatinginadvertently, means for attaching said fuze to a grenade body, and adetonating means for actuating a main explosive charge, wherein theimprovement comprises: a fuze head having a threaded bore communicatingwith said primer; a pyrotechnic delay cord; a solid cylindrical mandrelhaving a peripheral helical thread on its longitudinal surface extendingfrom one end of said mandrel to the other end; a mandrel-delay cordsub-assembly consisting of said delay cord wound upon said peripheralhelical thread; a detonator-delay assembly having said detonating meansattached to said mandrel-delay cord sub-assembly so that saidmandreldelay cord sub-assembly partially protrudes out of saiddetonating means providing a screw like extention, said delay cordinterfitably engages said threaded bore when said detonator-delayassembly is screwed into said threaded bore, said detonating meanshaving a shoulder which permits said mandrel-delay cord assembly to bescrewed into said threaded bore for a predetermined fixed distance. 2.An improved hand grenade fuze as recited in claim 1 wherein thepyrotechnic delay cord comprises: delay core; and a metal sheathlongitudinally circumambient to said delay core composition having openends exposing said delay core to said primer on said one end of saidmandrel, and exposing said delay core to said detonator on said otherend of said mandrel.
 3. An improved hand grenade fuze as described inclaim 2 wherein said metal sheath is aluminum.